1. Field of the Invention
This invention relates to coated solid detergent components and to detergent compositions containing these coated components. More particularly, the invention relates to detergent compositions which release one or more of their ingredients to the wash liquor with delay and under control, the release of these ingredients being controlled through the pH value of the wash liquor.
The controlled release of individual detergent components at certain stages of the washing process is both economically and ecologically advantageous and, accordingly, is the subject of intensive research. Whereas, in principle, each individual detergent component can be released at a certain time through suitable physical and/or chemical measures, this controlled release is of paramount importance above all with regard to the interplay between bleaching and enzymatic cleaning. Accordingly, most publications are concerned with solving the problem of separating bleaching and enzymatic cleaning from one another as a function of time because the aggressive bleaching agents deactivate or even destroy enzymes. In principle, there are two ways of achieving this, namely: delayed release of the bleaching agents so that enzymatic cleaning is over before the bleaching agents are released into the wash liquor and delayed release of the enzymes when the bleaching process is almost at an end. Since the bleaching agents destroy excess enzyme and thus prevent it from remaining on the laundry (odor formation), the first alternative is generally adopted. Another advantage of coating particles of bleaching agent lies in the increased stability in storage because uncoated bleaching agents are rapidly hydrolyzed in the event of prolonged storage, especially in moist air, with the result that the detergent compositions lose washing power.
Numerous ways and means are available for coating detergent ingredients. Various factors, such as the temperature or the hydrolysis of the coating material, may be utilized for the release process, depending on the particular solution adopted. Melt coating, in which the shell or coating only becomes permeable beyond a certain temperature, is difficult to achieve on account of the low washing temperatures preferred today because problems, such as lump formation, occur at low softening temperatures. Coating materials which hydrolyze under the effect of moisture also have disadvantages in regard to the stability in storage of the composition. Accordingly, there is a need to find a coating material which, on the one hand, would dissolve quickly without affecting the washing process providing certain conditions are maintained in the wash liquor and which, on the other hand, would be so stable that storage would not present any problems.
2. Discussion of Related Art
Detergent and bleaching compositions which contain a hydrogen peroxide source and a peroxy acid bleach precursor (bleach activator) and which produce an initial pH value in the alkaline range (pH 10-11) in the wash liquor and the delayed release of acid into the wash liquor to achieve a reduced pH value therein are described in the prior art literature, cf. for example European patent applications EPA-0 290 081 (Unilever) and EP-A-0 396 287 (Clorox).
The delayed release of individual components in bleach-containing detergent compositions is mentioned in a number of patents. International patent applications WO 95/28454 (Procter & Gamble) and the series from WO 95128464 to WO 951284469 (all Procter & Gamble) and WO 95128473 (Procter & Gamble) disclose bleach-containing compositions which contain a hydrogen peroxide precursor and a peroxy acid precursor, the release of the peroxy acid being controlled so that 50% of the peroxy acid concentration (so-called T50 Test) is reached within 180 to 480 seconds. The controlled release of the ingredients is achieved by coating individual ingredients, defined particle sizes, compacting and mechanical or manual addition. The particular ingredients coated vary from one application to another. Thus, in WO 95/28464, the release of the peracid is delayed in relation to the release of a complexing agent; in WO 95/28465 the release of the peracid is delayed in relation to the release of a builder and, in WO 95/28467, an enzyme is released before the peracid. WO 95/28466 describes the delayed release of an enzyme in relation to the release of a surfactant while WO 95/28468 and WO 95/28469 describe detergent compositions in which the release of an enzyme is delayed in relation to the release of a complexing agent for heavy metal ions or in relation to the release of a water-soluble builder. The systematic controlled release of individual components by controlling the pH value is not mentioned in any patent application of this series.
The coating of bleaching agents or bleach activators is also known from the prior art. U.S. Pat. No. 5,000,869 (Safe Aid Products) describes detergent compositions containing a coated halogenated glycol uril compound which is released through pH control. In this detergent composition, the bleaching agent is coated with a polymer which dissolves at a pH value above 6 and preferably at a pH value of 7.2 to 11.
WO 94/15010 (Procter & Gamble) discloses the coating of TAED with water-soluble acidic polymers, the coating being applied in the form of a melt, by spraying or in the form of solutions and dispersions, and also describes the simultaneous use of percarbonate which, in a preferred embodiment, is also coated. The acidic polymer has a solubility of at least 5 g/l at 20.degree. C.
EP-A-0 651 053 (Procter & Gamble) describes detergent compositions which contain an alkali metal percarbonate coated with alkali metal sulfate and carbonate, a bleach activator and a (coated) acidifying agent to be released with delay, so that the pH value of the wash liquor (1% solution at 20.degree. C.) is initially 9.5 to 13, falling to pH 7 to 9.3 after the acidifying agent has been completely released. The time required for complete release of the acidifying agent is between 30 seconds and 10 minutes. It is only when the pH value falls below a certain threshold that the coating of the bicarbonate is attacked and dissolved so that the bleaching effect is developed.
Coated bleaching agents which are only released into the wash liquor at an increasing pH value are not described in the prior art.
Now, the problem addressed by the present invention was to develop a system which would enable detergent ingredients, more especially bleaching agents, to be released through pH control and which would allow the release of those ingredients to take place in alkaline medium.